Cosmetic compositions of various kinds are widely used by consumers. Skin care cosmetics such as moisturizing lotions or creams are applied to obtain benefits of anti-aging, skin lightening and moisturizing, while make-up cosmetic products are applied to obtain desired optics and color benefits. Make-up cosmetics such as foundation and blemish-balm creams are able to deliver such covering and color benefits as a result of very high pigment and colorant content. Unfortunately, however, such high loadings can lead to an undesired feature of poor tactile sensory and for this reason moisturizers typically maintain low pigment dosage. It is the current trend that more and more make-up products are promoted to have moisturizer type in-use sensory and traditional moisturizers are formulated to deliver more perceivable optical benefits.
Whitening and opacifying optical properties delivered from moisturizer-type products generally come from their intrinsic emulsion structure (either W/O or O/W) and included particles with high refractive index, such as micronized titanium dioxide and zinc oxide. When topically-applied such products are usually spread to a very thin film (typically ˜20 micron thickness) on the skin surface. This film is subject to a fast drying process during which emulsion droplets coalesce and break up and opacifying particles aggregate. As a consequence, the film loses most of its optical benefits within minutes after application. Thus, in order to compensate the time-dependent loss of optical benefits, a high level addition of the opacifying particles may be included in the formulation. However such heavy loadings typically bring unnatural whiteness on initial application and are therefore not an ideal technical solution.
The present inventors have thus recognized that there remains a need to provide cosmetic compositions that are capable of providing benefits, especially optical benefits, which are long lasting and/or actually increase with time after application. The present inventors have found that such a need may be met by providing particle actives with particular configuration and properties. In particular the inventors have found that particles with a shell formed from inorganic material having a specific refractive index and filled with a volatile material having a specific refractive index can meet such a need.
The application of inorganic core-shell particles in cosmetics has been described. In particular the use of such particles for encapsulating active materials has been described.
U.S. Pat. No. 7,758,888 (Sol-Gel Technologies Ltd.) discloses a therapeutic, cosmetic or cosmeceutic composition for topical application, capable of stabilizing an active ingredient and delivering the active ingredient, comprising a plurality of microcapsules having a core-shell structure. The microcapsules have a diameter of approximately 0.1 to 100 micron. The core of each microcapsule includes at least one active ingredient and is encapsulated within a microcapsular shell. The shell is comprised of at least one inorganic polymer obtained by a sol-gel process, and the shell protects the active ingredient before topical application and is designed to release the active ingredient from the microcapsules following application. The composition is said to be useful in encapsulating active ingredients, such as benzoyl peroxide, that are unstable in other formulation, or are irritating to the skin.
WO 2011/076518 A (EVONIK DEGUSSA GMBH) discloses a powdery composition comprising: a) at least one powder in form of core-shell particles, the core comprising liquid water or a liquid aqueous phase and the shell comprising hydrophobic or phobized particles and b) at least one powder comprising carrier and b1) at least partially water soluble liquid and/or b2) a water reactive substrate each located in and/or on the carrier. Provision of such compositions in a powdery form allows the particles to break upon application to the skin and so the particles are not in the form of core-shell particles after application.
The foregoing publications do not recognize the utility of particles with a shell having a certain refractive index and filled with a volatile material also having a certain refractive index in providing cosmetic compositions that are capable of providing optical benefits to the skin, especially which benefits are long lasting and/or actually increase with time after application. Furthermore the publications do not recognize the utility of applying such particles in cosmetic compositions comprising hydrophobic material but with relatively low contents of liquid oil.